Daniel,
if the children learn why a thing (in this case, why the balloon didn’t pop) happens as a result of an activity, then that activity is a great starter for a deeper inquiry. In the inquiry activity that is child-centred, they can use their understanding to make predictions, observe results and then verify their own science knowledge.
In the case of Balloon Kebabs, with an older class you might share a version of these theories as to why it works, and ask them to work out a way to verify which is true:
Physics to Go #12
Balloon kebabs
1… Most of the balloon is stretched evenly, but there
are two points where it is less stretched, and where the
surface tension is at its lowest: the tied section and the
darker patch at the opposite end of the balloon. Most of
the balloon is under high tension, so attempting to push
the skewer through just makes the balloon pop. However,
at the low tension sections it is possible to make a small
hole without breaking the overall surface of the balloon.
2… You have to use a special type of kebab skewer
to make this trick work. Because these skewers are made
of bamboo, they secrete a very thin layer of oil. When this
oil comes into contact with the balloon, it reinforces the
surface making it stronger and enabling us to make a hole
without popping it.
3.… This trick only works if you do it really slowly.
By pushing the skewers very slowly into the balloon, the
molecules that make up the rubber of the balloon don’t
notice its presence. The skewer can therefore slip past the
molecules, making a hole before they have a chance to
react and make the balloon pop.
Source: https://www.iop.org/sites/default/files/2020-01/WI-physics-activity-pack.pdf
I couldn’t find Balloon Kebab on Marvin and Milo, but did find it in Physics to Go, where it is no. 12.